Abstract
A study of Mn-site substitution by Ni2+ and the effect of annealing time in polycrystalline bulk La0.7Sr0.3MnO3 in composition range (0 ≤ x ≤ 0.1) is presented. This study involves structural, electrical, magnetoresistance, and thermoelectric power (TEP) measurements. X-ray diffraction was used to examine the structure for the as-prepared and annealed samples, and it shows that there is no change in structure with annealing time. Electrical resistivity and magnetoresistance are strongly affected by annealing process, where there is a dramatic increase in resistivity with annealing time and an enhancement in magnetoresistance in different temperature ranges. Moreover, conduction mechanisms above and below transition temperature (Tms) are discussed, since, variable-range hopping and small-polaron hopping models are applied above Tms, in addition to some experimental relations below it. In addition, the TEP sign changes from positive to negative with doping and annealing.
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